This invention relates in general to measuring devices and more particularly to an apparatus for determining the rating of a torsion bar.
The handling characteristics of race cars depend to a measure on the stiffness of the suspension systems for such cars. Moreover, track conditions and configurations vary, each requiring a suspension system tailored to it. For example, dirt track races always proceed counterclockwise around an oval track, so all of the turns are left turns. Drivers prefer to stiffen suspensions at the left front and right rear wheels of their cars. This improves both control and traction.
The suspension system of a typical sprint car has four torsion bars—one for each wheel. The bars extend transversely across the vehicle, with two ahead of the front axle and two behind the rear axle. While the bars are traditionally classified by size, many drives prefer to classify them by rate, and one rate that has found acceptance is the amount of force required to deflect a torque arm at one end of a bar one inch. Thus, a bar rated at 235 lbs. would be stiffer than one rated at 197 lbs. Rates may vary among bars of the same size. Each torsion bar exerts a downwardly directed force on the axle near the wheel with which it is identified and an upwardly directed force on the frame of the car at the corner where the wheel is located, thus suspending much of the weight of the vehicle. The bars are accessible at the ends of the car and require little effort to remove and replace. Often a driver will replace an entire set of bars with a new set more suited for the conditions of a forthcoming race. However, before a driver replaces any torsion bar, he should know how it will react in the race car, and this depends on the spring rate for the bar.
Testing devices exist for comparing torsion bars of a set or in collection at a driver's disposal. Indeed, manufacturers of torsion bars sometimes apply ratings to them, but the ratings may not correlate to the ratings used or acquired elsewhere, and furthermore may not be accurate. In any event, the testing devices used by manufacturers are much too large to be used by individual drivers, particularly at the tracks where they race. Another testing device exists which is suitable for use in a shop, but is not easily transported to a track, and furthermore is expensive. Still another testing device is available which is small enough to transport to a track, but does not rate bars according to any recognized standard. Moreover, the devices currently available twist the bars in only one direction of rotation, but the rates of some bars vary, being of a magnitude in one direction of rotation that is different than the magnitude in the opposite direction.